Roof curbs are widely used in the air conditioning industry as foundation supports for air conditioning units mounted on the tops of roofs of buildings. The curbs are typically "roofed" into the roof by roofing material. The roof curbs are normally constructed either as a single unit comprised of welded together sides and end sections, or as components which are bolted together on the roof, before roofing in the curb and then placing the air conditioning unit on the assembled roof curb.
The difficulty with a roof curb that has been welded together at the factory and transported to the roof site is that the roof curb, which can typically vary anywhere from three to eight feet in width, and four to twenty-five feet in length, must be shipped as a unit thereby incurring high shipping costs. Also, heavy equipment must be used to raise the welded roof curb into location on the top of the roof. The advantage of the unitary construction is that it is square and always thus fits the air conditioning unit. Once the curb is roofed into place with roofing materials, the air conditioning unit can be moved into place on the roof curb.
A difficulty with roof curbs which are constructed of components which are bolted together is that a tradesman is required to bolt the components of the roof curb together on the roof of the building. This process typically takes at least an hour. Bolted curbs are not always practical because often inclement weather prevents the tradesman from bolting the roof curb components together in a timely fashion. Also, curbs which are bolted together may not always be square. If the non-square bolted curb is "roofed in", and the air conditioning unit is found to not fit the curb, then the roofing must be removed, the curb squared up, and then reroofed. This is expensive and time consuming.
The advantage of bolted roof curbs is that they can be hauled or lifted to the roof site as separate components, and the components bolted together in place on the roof. The roof curb components can be shipped in disassembled form, which greatly reduces freight costs. There is no need to use heavy hauling and lifting equipment.
U S. Pat. No. 4,501,193, Snyder, Feb. 26, 1985, discloses a mounting curb for rooftop packaged air conditioning units comprising a generally rectangular frame having a bottom wall with adjacent return and supply air duct openings formed therein and in communication with respective common supply and return air ducts formed in the curb. The return air duct includes opposed branch portions leading to openings in the top wall of the curb in communication with the return air openings in the air conditioning units. The supply air duct includes opposed branch portions also in communication with respective supply air openings in the bottom wall of the air conditioning unit enclosures. The supply air duct is disposed generally over the return air duct and inward therefrom with respect to the opposite end walls of the curb.
U.S. Pat. No. 3,721,106, Bierwirth et al., Mar. 20, 1973, discloses a rectilinear upstanding, continuous, rigid curb on a flat rooftop which defines an opening through the roof. Vibration isolation means are supported on the top of the periphery of this curb and, in turn, support the main frame of a complete air conditioning unit. The vibration isolation means includes a continuous sheet of flexible material in sealing relationship to both the entire lower outer periphery of the air conditioning unit frame and the entire upper outer periphery of the curb, and loosely disposed between the curb and frame. This sheet isolates the inside of the air conditioning unit and building from the outside thereof, and insulates the space within the curb and the unit from the temperature and weather conditions outside.